306 



HORMONES 



being offered new-born baby rats for adoption. In most instances the females remain 

 indifferent to the intruders. But if, to these nonchalant misses, a few doses of pro- 

 lactin are administered, not only are their mammary glands stimulated but a remark- 

 able change in their behavior takes place. They will now eagerly adopt as many 

 babies as may be offered, build elaborate nests for them, and eagerly mother them. 





Iteproduced by permission from TuriUT, (Iciicidl i:niluciin(j}ii(nj, W. B. Saunilers 



('omi)an.v. 



Fig. 11-5. Acromegaly. 



The yearning seems to be universal. Their maternal reactions are not confined to 

 infants of their own kind but are extended to baby mice, baby rabbits, or even 

 helpless squabs. For a normal, vigorous rat to do other than promptly make a feast 

 of a proffered squab is proof positive that something fundamental has happened 

 to her instincts. What part prolactin may play in the determination of human 

 instincts and emotions is as yet unknown, but the stimulus to imagination is 

 tempting." 



Gastrointestinal hormones 



The secretion of digestive juices and the movements of the stomach 

 and intestines incidental to the digestion of food are partly controlled 

 and regulated by several gastrointestinal hormones. These processes 

 are also influenced markedly by nervous stimulation, and it has been diffi- 

 cult to sort out the two types of effect. At present four gastrointestinal 

 hormones have been quite definitely proved to exist, and a number of 

 others are suspected. None of them are definitely known to be essential 

 for life or to cause any disease if produced in abnormally large or small 

 amounts. 



Before considering these substances in detail, a distinction should be 



